Over 500 BTC Hack: Coldcard MK3 Security Advisory & Complete Protection Guide
Over 500 Bitcoin have recently been stolen in a security exploit affecting older Coldcard MK3 hardware wallets. Here is the full breakdown of what happened, who is affected, and the exact steps you must take right now to protect your Bitcoin.
Watch on YouTube · Emergency Breakdown & Migration Advice by ForrestHODL
You are SUSCEPTIBLE to this exploit if you meet ALL of the following criteria:
- You generated your seed phrase on a Coldcard MK3 (or older MK2 model).
- The seed was generated after firmware version 4.01.
- You generated the seed phrase on-device without using physical dice rolls.
- You did NOT use a passphrase (or used a very weak 2–3 word passphrase).
1. What Happened? The 500+ BTC Coldcard Exploit
A major security situation has unfolded in the Bitcoin self-custody space. Over 500 Bitcoin have been drained across multiple compromised wallets associated with CoinKite's legacy hardware wallet model, the Coldcard MK3.
CoinKite issued an official security advisory stating that seeds generated on MK3 devices after firmware update 4.01 may suffer from compromised entropy in the device's random number generator (RNG).
Interestingly, attackers have not drained every compromised wallet completely—in many instances, partial amounts were swept. Emerging speculation suggests that attackers may be utilizing powerful Large Language Models (LLMs) or automated security scanners that uncovered this flaw in open-source codebase repositories, writing automated scripts to sweep vulnerable single-key wallets.
Note: This is an evolving story. While CoinKite initially noted that MK4, MK5, and Q devices appear unaffected, some independent researchers (including James O'Beirne, Pine, and zero_knowledge_goof) emphasize that any wallet generated without external entropy or multi-factor security should be re-evaluated promptly.
2. The Rule #1 Requirement: Do NOT Panic
If you own a Coldcard MK3, the single most important rule right now is: Do NOT panic and do not rush.
Historically, during emergency security events, far more Bitcoin is lost due to panic—users making typos in addresses, pasting seed phrases into phishing sites, or improperly handling backups—than from the exploit itself.
Immediate Safety Checklist
- Check your wallet in your watch-only coordinator (e.g., Sparrow Wallet) to verify that your funds are intact.
- Verify your hardware model and check when your seed phrase was generated.
- Confirm whether you added a custom BIP-39 Passphrase when initializing the wallet.
- Execute your migration strategy calmly and carefully, double-checking every address on your hardware display.
3. Action Plan: How to Protect Your Bitcoin
Depending on your available hardware and situation, choose the best migration pathway below:
Migrate to a New Hardware Wallet / Multisig
The gold standard resolution is to acquire a new hardware wallet (e.g., Trezor, Foundation Passport, or a newer Coldcard MK4/MK5/Q) and generate a fresh seed phrase incorporating physical dice rolls + a strong Passphrase, or set up a 2-of-3 multi-vendor multisig setup.
- Generates clean, verified high entropy outside of software reliance.
- Completely eliminates single-device hardware vulnerability risks.
Move Funds to a Passphrase-Protected Wallet
If you cannot immediately buy a new hardware wallet, create a robust BIP-39 Passphrase on your MK3. This creates a completely separate passphrase-derived wallet address set. Transfer all Bitcoin from your seedphrase-only wallet to this new passphrase wallet.
💡 Watch my step-by-step tutorial: How to Move Bitcoin from a Seed Phrase Only Wallet to a Passphrase Wallet Using One Hardware Wallet.
Destroy Seed & Re-generate Using Casino Dice Rolls
Physical dice rolls sidestep hardware RNG flaws completely by introducing real-world physical entropy.
- Verify your current seed backup written on paper/steel.
- Navigate to Settings → Danger Zone → View Seed to cross-reference line by line.
- Select Destroy Seed in seed functions.
- Power on the Coldcard, select Create New Wallet, and choose Dice Rolls. Roll physical dice to manually supply 100+ rolls of entropy.
Temporary Software Wallet or Custodial Transfer
If your MK3 is active and you have zero other hardware options, temporarily sweeping funds to a desktop software wallet (like Sparrow on clean desktop OS) or a secure exchange account is acceptable purely as a short-term emergency step while acquiring proper cold storage.
4. The Math Behind Passphrase Security
If your MK3 seed phrase was vulnerable, your passphrase is currently doing 100% of the heavy lifting to secure your funds against brute-force attacks.
Security researcher Pine published a helpful compute benchmark demonstrating why passphrase complexity and length matter immensely when attackers attempt brute-force checks (assuming 100 million attempts/sec costing ~$33–$66/hr in rental compute):
| Passphrase Complexity | Time to Brute-Force | Estimated Cost to Crack |
|---|---|---|
| 3 BIP-39 Words | ~43 seconds | $40 – $80 |
| 4 BIP-39 Words | ~24.5 hours | $800 – $1,600 |
| 7 BIP-39 Words / Custom Complex Phrase | 23.9 Million Years | $7 Trillion – $14 Trillion |
Takeaway: Do not use short 2 or 3-word passphrases! Treat your passphrase as a true phrase—incorporate uppercase, lowercase, numbers, special characters, or 6+ random words.
5. Updates & Policy Changes from ForrestHODL
In light of this evolving advisory, I am taking immediate proactive steps across all my channels:
- Affiliate Link Removal: I have removed all Coldcard affiliate links from my YouTube video descriptions and website until clear, verified resolution details are fully confirmed.
- Wallet Hardware Reviews: I am conducting thorough security reviews of alternatives like Trezor and Foundation Passport, assessing cross-vulnerability risks across open-source hardware ecosystems.
- Direct Support Commitment: If you are overwhelmed or worried about losing funds during migration, reach out directly. I am answering community emails and offering 1:1 sessions to guide you through safely step-by-step.
Need 1:1 Assistance Securing Your Bitcoin?
If you want personalized, step-by-step guidance migrating your seed phrase, setting up passphrase protection, or configuring a multi-vendor multisig setup, book a private coaching call with ForrestHODL.
Book a 1:1 Coaching Session